The use of batteries as an alternative source of energy is promoted in a variety of applications, including in the automotive industry. At the same time, there are a number of challenges that currently inhibit a large scale implementation of batteries as an alternative source of energy in industry, in particular in the automotive industry. Those challenges include both technical problems and challenges in overcoming an inertia in an industry which over many decades has been dominated by engine designs based on fossiled energy resources, in particular fuel and more recently gas based energy sources.
In an attempt to overcome those challenges, hybrid electric vehicles (EVs) have been proposed and are starting to be implemented commercially. Hybrid EVs, as the name suggests, utilize a conventional engine design, in conjunction with an electric motor system to supplement the conventional engine. In some designs, the electric motor may temporarily be utilized as the sole provider of the vehicles' movement under specific operational conditions.
In the design and implementation of such hybrid EVs or pure EVs, it is crucial to accurately determine the SOC of the rechargeable battery during the continued use of the hybrid EV. Typically, the SOC is monitored via on-board monitoring circuitry, which effectively integrates the continuous charge and discharging capacities of the battery in operation.
However, it has now been recognized that such circuitry can only provide sufficiently accurate data and over a sufficiently long period of time under non-critical operating conditions. Such non-critical conditions refer to the operation of the electric motor at e.g. constant speeds, and during slow or moderate accelerations and decelerations. Also, it has been recognized that the battery charge and discharge characteristics and performances are greatly affected by the environmental conditions, such as temperature and pressure, during the operation or use of the battery.
The reliance on such non-critical operating conditions is not satisfactory for many applications, including the application in hybrid EVs. In such applications, the operation conditions often include the use of the electric motor under high acceleration conditions, in particular at high initial mechanical impulse, such as quick start, overtaking on a freeway, or during steep inclines. For such operating conditions, the monitoring of the SOC of the rechargeable battery in an accurate manner is crucial, to reduce or eliminate the risk of polarity reversal or over discharge of a rechargeable battery. Also, when a cruising hybrid EV or pure EV is braked, large amount of kinetic energy will be converted to electrical energy when regenerative braking is applicable, for fast charging the batteries. Risk of over charging may occur if correct SOC is not known.
In at least preferred embodiments, the present invention seeks to address one or more of the above mentioned concerns in relation to the determination of the SOC of a rechargeable battery.